July 19, 2010 -- AIDS researchers have finally found a vaginal gel that halves a woman's risk of getting HIV from an infected sex partner.

The announcement, made at the outset of the 18th International AIDS Conference in Vienna, Austria, marks the beginning of the end of a 20-year search. Those years saw the failure of 11 clinical trials of six different agents intended to help women avoid HIV infection.

Now a vaginal gel containing tenofovir, an anti-HIV drug sold as Viread by Gilead Sciences Inc., is the first shown to protect against infection with the AIDS virus.

The announcement was made by husband/wife researchers Quarraisha Abdool Karim, PhD, and Salim S. Abdool Karim, MD, PHD, of the Center for the AIDS Program of Research in South Africa (CAPRISA) and Columbia University.

"We now have a product that can potentially alter the epidemic ... and save millions of lives by averting HIV infection," Quarraisha Abdool Karim said at a news teleconference.

She asked reporters to imagine a young woman in rural South Africa whose partner is a migrant worker who refuses to use a condom and will not allow her to use the female condom.

"Picture [that woman] asking what I have to offer to prevent her from getting infected with HIV," Abdool Karim said. "Until today I had nothing to offer. Today that changes. I can now offer tenofovir gel that offers 39% protection. And if she is highly adherent, it can be up to 54% protection."

That's far from full protection. But given that about 10% of the population in the area where the gel was tested are infected with HIV, such protection would have a profound effect.

"Without the gel, for every 100 women, 10 will be infected in a year. With this gel, only six women will be infected," Quarraisha Abdool Karim said. "For an individual woman, we say, 'If you use it consistently, you cut your chance of infection in half."

If one in three South African women at risk of infection use the gel, she estimated, over 20 years there would be 1.3 million fewer HIV infections -- and 820,000 lives would be saved.

The gel is applied 12 hours before sex and again 12 hours later. Salim Abdool Karim said that while this should be done only once every 24 hours, the gel should theoretically offer protection to women who have sex more than once during that time.

Vaginal Anti-HIV Gel: Confirmation Needed

As welcome as the findings are, the study by the Abdool Karims and colleagues must be confirmed. The study gave the gel to 445 sexually active women in rural and urban South Africa, while 444 women received identical, inactive placebo gel.

Over the course of the study, 38 women who got the gel and 60 women who got the placebo became HIV infected. Overall, that's 39% effectiveness. But women who used the gel in at least 80% of sexual encounters had a 54% prevention rate.

If the gel truly works, however, Salim Abdool Karim believes that women will be much more likely to use it than they were in the study, during which they were warned not to rely on it and that it's safety was unproven.

In terms of safety, the gel did not have negative side effects. Virus in women who became infected with HIV despite gel use was not resistant to Viread.

While the Abdool Karims' study must be confirmed, the findings suggest that they used the right approach. By spiking the gel with a drug that enters cells and repels HIV when it tries to enter them, they took a different tack than previous gels which used general microbicides to kill HIV on vaginal surfaces.

The U.S. National Institute of Allergy and Infectious Diseases (NIAID) already has launched a study to confirm the efficacy of tenofovir gel.

"The NIAID-sponsored VOICE study, which launched last fall and is expected to enroll 5,000 women in four south African countries, will provide additional safety and effectiveness data for a tenofovir-based vaginal gel as an HIV prevention method," NIAID director Anthony Fauci, MD, says in a news release. "The study also will offer some insight as to the gel's acceptability as a product used once a day rather than one that is used before and after sexual intercourse."

Anti-HIV Gel Protects Against Genital Herpes, Too

There's an additional benefit to the tenofovir gel. Salim Abdool Karim reported that it also protects against genital herpes infection -- which itself makes a woman more susceptible to HIV infection.

"We also show a 51% reduction in HSV-2 [genital herpes] infection," he said. "Women who have HSV-2 have twice the risk of acquiring HIV. So this would have the benefit of reducing risk of HIV in women who otherwise would have acquired HSV-2 infection."

Abdool Karim said that Gilead has promised him that it will allow South Africa to manufacture tenofovir gel without having to pay any royalties to the company.

The Abdool Karims and colleagues report the findings in the July 20 online journal ScienceExpress.